The present invention is directed to a clamping mandrel for the rotatable support of a web wound on a tube.
Clamping mandrels usable for the rotatable support of paper rolls, such as are used in connection with web-fed rotary printing presses, are known from U.S. Pat. No. 4,149,682, U.S. Pat. No. 4,951,894 and U.S. Pat. No. 4,715,553. Ejecting devices are provided on the clamping mandrels, by use of which the tube on which the paper web is wound can be stripped off the clamping mandrels. Spring elements, that are provided on the ejecting device, are elastically prestressed in the course of inserting the clamping mandrel into the tube. When the clamping mandrel is pulled back out of the tube for changing the paper web, the prestress of the spring elements assures that the tube is stripped off the two oppositely located clamping mandrels.
The disadvantage of this type of structure of an ejecting device lies in that the force, by which the tube can be stripped off the clamping mandrel, is limited by the type of construction of the spring elements. It is moreover necessary to overcome the prestress of the spring elements in the course of inserting the clamping mandrels into the tube.
A clamping mandrel is known from DE 28 14 338 A1, in which a displaceable ring, which can rotate together with the mandrel, is arranged between the detent flange of the mandrel and the tube. An actuating device, which is fixed in place on a frame, is provided for ejecting the tube. Claws are provided on the actuating device, wherein the ring can freely rotate in one position of the claws, namely the position of rest, and is not in engagement with the claws. In the course of operating the actuating device the claws are pressed against the ring, so that the tube can be stripped off the clamping mandrel.
It is disadvantageous in connection with the actuating device known from DE 28 14 338 A1 that, because of its mechanical drive mechanism, the ejecting device requires a large structural volume.
DE 35 36 1777 C1, DE 29 48 753 A1, U.S. Pat. No. 2,826,376 and JP 53-051 371 A describe devices for receiving a wound roll.
It is the object of the present invention to provide a clamping mandrel.
In accordance with the present invention, the object is attained by providing a clamping mandrel for the rotatable support of a web which is wound on a tube. An ejecting device is usable to strip the tube off the mandrel. The ejecting device includes at least.
The advantages which can be achieved by the present invention lie, in particular, in that a pressure-charged piston is employed for driving the ejecting arrangement. Since the pressure-containing fluid, which may be, for example, compressed air or hydraulic fluid, can be conducted to the piston head above the piston through conduits, whose geometry can be arbitrarily designed, clamping mandrels of very compact design are possible. It is furthermore possible to generate very high stripping forces by selecting a correspondingly high working pressure.
To reduce the technical outlay, in the course of constructing the clamping mandrel, it is advantageous if the piston for stripping off the tube is driven by use of the fluid. Elastic spring elements, for example helical springs, can be used for restoring the piston into the initial position.
Since the ejecting arrangement has an element, which can be rotated along with the clamping mandrel, and a fixed element, which two elements must be brought into engagement with each other, there is the danger that increased wear may occur in the area of contact between the rotatably seated element and the stationary element of the ejecting arrangement. Therefore, the embodiment of the ejecting arrangement is to be selected so that the second element can be switched between a position of rest and at least one working position. In the position of rest, the first element is completely separated from the second element by a gap, while in the working position the first element comes to rest against the second element, so that forces for actuating the second element can be transmitted.
Magnetic elements can be particularly advantageously employed for restoring the second element out of at least one working position. The attracting forces, emanating from a magnetic element, act in a contactless manner over an air gap, and in this way they can automatically retract the stationary second element, for example an actuating piston, in a particularly simple manner.
In general it is advantageous, in connection with devices which have a rotatably supported and axially actuable adjusting element, which adjusting element can be displaced by an axially displaceable, fluid-driven piston between a position of rest and at least one working position, if the axially displaceable, fluid driven piston can be returned from its working position into its position of rest by use of at least one magnetic element. It is possible, in this way, to prevent wear in the contact zone between the fixed piston and the rotatably supported seated adjusting element in a simple way. As long as it is not needed, the piston is automatically retracted, in a simple manner, by the magnetic element and is dependably maintained in its retracted position .